The mechanisms and regulation of chromosome replication and cell division in E. coli will be examined by studying autonomous plasmid replication, and the division cycle of dnaAts mutants growing under integrative suppression. The studies on autonomous plasmid replication are designed to determine 1) the timing of replication of large F' plasmids in relationship to chromosome replication in three substrains of E. coli B/r growing at various rates, 2) the timing of replication of an F'lac plasmid in a cell which contains a deletion of the lac region of the chromosome, 3) alterations in the relationship between chromosome replication and cell division which are consequences of the presence of large, autonomously replicating plasmids in the cells. The studies on the dnaAts mutants growing at nonpermissive temperature due to suppressive integration of F' plasmids are designed to determine aspects of the coupling between chromosome replication and cell division. A variety of dnaAts alleles of E. coli B/r F, which are capable of being synchronized by the membrane-elution technique, will be suppressed by integration of F' plasmids at various regions of the chromosome. Experiments with the membrane-elution technique will be used to be used to determine 1) the sequence and rate of chromosome replication, 2) cell age at initiation of chromosome replication, and 3) the lengths of the C and D periods and the relationship between chromosome termination and initiation of cell division. It will also be determined whether the normal chromosomal terminus is a specific site on the chromosome at which replication always terminates to yield cell division, or whether termination takes place when the two replication forks meet.